Abusive parents please help!?

Ohkay, so this has been going on for quite a while I don't wanna talk about it with my sister because I don't wanna scare her, anyways my parents are constantly arguing that in fact I actually think they should get divorced. Well it's gotten to the point where my dad started hitting my mom and not like where it leaves a bruise but like slapping her arm. And I hear my mom say stop it hurts and he'll just be like good you had no right to say that... I cry myself to sleep almost every night not being able to get my moms scared voice out of my head. This is the second time the first time my dad grabbed my moms arm quite hard and left a bruise. Now I know what you'll are thinking that my dad is this evil monster, no, he's very nice playful, kind, funny, but I know he also drinks a few beers at night everynight. Anyways who can I talk to this about because it's not only hurting my mom it hurts me and alot, the first my dad hit her I cut myself saying 'mom the same pain you feel, I do also' I pray every night begging God to save our family, please who can I talk to about this. Besisdes family members.